Offline air pollution monitors (2)

Caroline Russell: Air pollution monitors in London, particularly the one on Brixton Road, have been offline for not just hours but several months in 2019. Given you use this data to model effectiveness for programmes like the Ultra Low Emission Zone (ULEZ), how will this impact your ability to monitor the results of the ULEZ and wider air pollution programmes at key locations?

The Mayor: London has one of the most comprehensive air quality monitoring networks in the world. Our analysis of preliminary data for the reference network (see MQ2020/0043) in 2019 shows 95 per cent of NO2 sites achieved the minimum capture rate required for assessment purposes in 2019, with 96 per cent for PM10, and 91 per cent for PM2.5. This high-level performance across the network is sufficient to identify trends and impacts of policies such as the ULEZ, our ability to do this has not been impacted by monitors being offline.
Recent examples of the way that London’s air quality monitoring network is used include the ULEZ 6 month report (https://www.london.gov.uk/sites/default/files/ulez_six_month_evaluation_report_final_oct.pdf) where the network recorded a reduction of over a third in roadside concentrations of NO2 in the zone.
In addition, we have supplemented the reference grade monitoring with over 100 sensors and mobile monitoring as part of the new Breathe London network. The boroughs also measure nitrogen dioxide at over 1000 locations across London using diffusion tubes. The London Atmospheric Emissions Inventory also models pollution levels across the entire city. This additional capacity enables us to better understand hotspots at key locations.
Brixton Road went offline on August 2018 when the station flooded during heavy rain. Lambeth council had a series of issues with contractors, suppliers and utility companies which meant the site was not functional again until April 2019. Since then it has been reliably recording data with the exception of a short period (18 – 22 July 2019) when it was taken offline as a precaution when a contractor suspected there had been another leak, which proved to be a false alarm.